Ian M's Lathe Notes

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Currently these notes are semi-organized and non-authoritative. As I become more experienced with the RML CJ18A mini-lathe, I'm cleaning up, extending and reorganising them. If in doubt, *ASK*, preferably your lathe induction trainer for an authoritative answer, though I may be able to help . . .

The Lathe

All Chinese 7x10 to 7x16 mini-lathes seem to be remarkably similar (not uncommon with Chinese products due to Shanzhai (山寨) ) and the OEM of our Amadeal CJ18A Mini-Lathe is/was probably Yangzhou Realbull Machinery Co. Ltd. Very similar lathes are also made by Sieg, but their lathes tend to be slightly less sophisticated than the equivalent Realbull models. N.B. Many Sieg parts are known to have slight but critical differences from Realbull parts, so *DON'T* order Sieg spares for a Realbull lathe!

Our Facilities page has:

Lathe

Lathe

In the kitchen.

Marked as a CJ18A Mini-Lathe from [Amadeal] [Manual]

Induction Document

Possible upgrades:

Please do not use the lathe until you have received induction

Key Specifications

Amadeal says the CJ18A Mini-Lathe is a 7x14 model with:

  • Power 550 W
  • Distance between centres : 350 mm
  • Swing Over Bed: 180 mm
  • Swing Over Cross Slide: 110 mm
  • Taper: MT3
  • Tailstock Taper: MT2
  • Chuck diameter: 100 mm
  • Spindle Speed: 50 - 2500 rpm (with digital readout)
  • Spindle Bore: 20 mm
  • Cross slide Travel: 65 mm
  • The lead screw is metric, pitch 1.5 mm.

Even though the compound and cross slide handwheels appear to be calibrated in thousandths of an inch, as ours is a metric machine, they only approximate that. One turn of the handwheel is 1mm advance, and they have 40 divisions, so each division is 0.025 mm, (approx. 0.984 thou).

Notable Accessories

We have:

Measuring Tools

We have:

  • Various dial indicators - the one with the adjustable magnetic base stand is the most convenient for most lathe setup work.
  • 25mm micrometer (in little grey case)
  • Grey case containing set of measurement tools including dial calipers, micrometer, steel rule (metric & inch) and engineers square

Change Gears

Custom puller for B-C stub shaft
Pulling the B-C stub shaft

See "Conquest Super Lathe" manual (below), section 4.7 Change Gears, PDF pages 28-29, but see below for mesh adjustment. The LittleMachineShop.com "Mini Lathe User’s Guide" (also below) section Threading gives a far better explanation, with pictures and diagrams, *BUT* its for a lathe with a US 1/16 inch pitch leadscrew, not a metric 1.5 mm pitch one like ours, so you *MUST* ignore all the tables in that section, replacing them with metric mini-lathe (with 1.5 mm pitch leadscrew) equivalents.

We have the following tooth count gears: 20,20, 30, 35, 40,40, 45, 50,50, 60,60, 80,80 which consist of the OEM power feed gears + the metric change gear set. Apart from the metal 20 tooth pinions, they are all plastic, probably Delrin if the molded in 'POM' marking can be trusted, but possibly plain Nylon 6.

If we wanted to add the capability to cut US/Imperial threads we'd need to buy additional 55, 57 and 65 tooth gears, and possibly a 21 tooth metal pinion.

CGTK's Change Gear Calculator (link preloaded with our gear list) is useful if you don't want to calculate the ratios from first principles. Not all suggested combos will physically fit.

  • Take care *NOT* to loose the keys in the A and D shaft keyways - turn the shafts till the keyway is up before removing the gear.
  • The B and C gears are coupled by a hollow stub shaft (with an integral key), which is so tight in the gears it has to be pressed or driven out - I've made a puller just for this task, kept in the change gears tin.
  • The center of the B-C stub shaft *MUST* be lubricated where it runs on the idler pin on the change gear banjo bracket, with grease or heavy oil. Seizure of the stub shaft due to running dry is a frequent cause of catastrophic mini-lathe geartrain failures!
  • Don't get oil on the change gears as it can cause plastic gears to crack. Only PTFE drylube or plastic compatible white grease should be used on their teeth.
  • Adjust the idler pin position in the straight slot first to set the C to D gear mesh, tighten its nut, then swing the whole banjo about the D shaft boss to set the A to B mesh, and finally tighten the banjo clamping nut.
  • Check both gear meshes has running clearance by turning the chuck by hand enough to complete one full turn of the leadscrew, and by attempting to turn the intermediate gear(s) to assess backlash, If excessive resistance is felt or if there's significant backlash, readjust the gears. If you have difficulty judging the mesh, a strip of 80 gsm copier paper (approx. 0.1 mm thick) wound into the meshing teeth before tightening the stud or banjo will give appropriate clearance once removed. Once setup, check the gears run quietly under power.
  • If the sum of the tooth counts C+D is the same as for the ones you just removed and they were correctly meshed, you don't need to move the stub shaft post. If A+B is also the same, you don't need to move the banjo. If it was set up for 1:1 reduction power feed, 1 mm (40:60 - 50:50) for M6 and 1.5 mm (e.g. 40:60:40) for M10 pitches can thus be achieved by only swapping gears.

Power Feed

When used for turning with power feed, the change gears should be set for a 16:1 reduction (A:20 : B:80 - C:20 : D:80) using the pair of small metal 20 tooth pinions and the 80 tooth plastic gears (largest in set), for a feed of 0.09375 mm per turn (1.5 mm/16). Unless continuing your threading project the next session, please re-fit the 16:1 power feed set after threading so the power feed is ready for use.

  • *ALWAYS* leave the feed direction selector lever in its neutral (no feed) position, and the half-nuts open after use.
  • *ALWAYS* check the carriage lock is disengaged before engaging power feed. Unlock the carriage after use.

ToDo: Check max distance between A and B-C shafts and B-C and D shafts to see if we could use 100 tooth gears for a finer power feed. As our gears are metric Module 1, the distance in mm between shaft centers equals the total tooth count of the meshing gears so we need 120 mm. Unfortunately the banjo plate clamping nut is closer than that so no go. Still need to measure the min. and max. distances to aid planning change gear selection.

Threading Dial

The threading dial is an aid to re-engaging the half-nuts at the right moment so the tool will retrace its previous path cutting deeper, rather than offsetting some fraction of the thread pitch and ruining your work. Its based on the concept of the lowest integer multiples of the leadscrew and thread (being cut) pitches that exactly match, but for mechanical simplicity it only covers certain selected multiples of the leadscrew pitch.

We have a choice of three pinion gears:

Threading dial Pinion Gears
Teeth Colour Dot Usable lines OD gear Dist. per turn
14 Red 1,7 7.51 mm 21 mm
15 Orange 1,5,9 8.05 mm 22.5 mm
16 Green 1,4,7,10 8.37 mm 24 mm (2 mm/div)

They are now colour coded, with a paint dot on the gear end face (the only non-wear surface). The 16 tooth one is normally left on the lathe, but disengaged when not threading to minimise wear on the lead screw. The others are kept in the Change Gear tin.

There's a threading dial 'pickup' calculator here: https://www.cgtk.co.uk/metalwork/calculators/threaddialindicator

Initially select Lathe: Sieg SC2 Metric to get most of our lathe's parameters, then select Custom, so you can enter:

  • Thread Dial Indicator Gear Teeth: 16,15,14
  • Line Marking: Every Line Numbered
  • Lines on Thread Dial Indicator: 12

Note the teeth list is entered in reverse order so the resulting table highlights any required pinion changes.

N.B. The dial is only friction clamped to the pinion by its center screw. If you have any reason to suspect it may not be properly aligned:

  1. With the power off and the carriage unlocked, engage the feed direction lever upwards. You'll probably need to turn the chuck by hand to get it to engage.
  2. If the threading indicator isn't already engaged, loosen the threading dial support block bolt, pivot the block to engage the pinion with the leadscrew and retighten the bolt.
  3. Engage the half nuts, again turning the chuck by hand till they drop in.
  4. Turn the chuck a couple of turns, top towards you to take up any backlash, then lock the carriage, taking care not to push it left while locking it.
  5. Loosen the screw securing the dial to the pinion.
  6. Align the '1' line of the dial with the index line, by rotating the dial clockwise, then retighten the screw.
  7. Don't forget to disengage half-nuts and unlock the carriage!

The above instructions should result in the half-nuts engaging cleanly when exactly on any valid line when threading towards the headstock. If it is required to thread away from the headstock, and the half-nut engagement point as seen on the dial is unacceptably far off the index line, follow them but reversing the feed lever, direction not to push the carriage and direction to turn the dial when aligning it.

Changing the pinion:

  1. Loosen the threading dial support block bolt and disengage from the leadscrew.
  2. Undo dial center screw, and remove it and the dial, dropping the old pinion out the bottom.
  3. Oil the shaft of the new pinion with a drop of light oil and insert it from below, gear end down.
  4. Refit dial and screw.
  5. Check the dial and pinion turn freely with minimal resistance.
  6. Align as above.

Turning

We are getting good results in aluminum and brass, and even steel using HSS cutting tools in quick-change tool holders, and the ~94 um/turn power feed. Unfortunately due to lack of rigidity in both the machine and smaller diameter parts, if you don't want the outer end to be over diameter, multiple 'spring' passes will be required.

A 'Speeds & Feeds' chart for HSS tooling, published by Model Engineer magazine can be found [here]. The second row is the target feed rate and the rest of the chart, apart from the diameter column is RPM.

How to do the maths to calculate speeds and feeds: https://www.cutwel.co.uk/blog/speeds-feeds-made-easy

Boring

Caution: As the spindle doesn't extend right through the headstock housing, if boring in a through hole, chips tend to fall out the back and tumble in the spindle bore till they fall into the change gears. To avoid this, one should plug the spindle bore with a wad of paper towel or rag and when cleaning up afterwards, use a rod to push it through towards the tailstock, with the chuck jaws (if fitted) wound clear of the spindle bore.

I haven't sorted out the boring tool situation yet. Both boring jobs to date have been bodge jobs with an awkwardly angled turning tool and achieving acceptable effective rake with enough clearance to reach deep enough into the hole has been problematic. I need to review the tools we have and see if any are suitable for starting out in a 13mm bore, the max diameter we can (easily) drill.

A swivel bladed hole deburring tool can be found in the main room on the windowsill behind the drill press.

Faceplate Work

Faceplate work is probably the most dangerous operation you can (or rather should) perform on a lathe. The working area is a large diameter spinning surface with protruding clamps to fixture the part that it is impractical to guard. Protruding clamps, studs, nuts etc. are very difficult to see at speed.

Treat the faceplate with great respect and caution if you wish to continue to be able to count to ten on your fingers!

I strongly advise reading chapter two of Tubal Cain's book "Workholding in the Lathe" several times before your first faceplate setup, and if possible get another experienced lathe user to check your first few setups before spinning them up.

Open ended/sided clamps should be oriented so that cutting forces drive the work towards the clamping bolt/stud, not out from under the clamp. Minimize the protruding length of thread past the clamping nut, if nessercery using sacrificial bolts or studs you can cut to length. Double-check all clamps are secure, manually turn the faceplate to check the work and clamps clear the ways, top-slide and toolpost, and stand out of the 'line of fire' (a disc extending from the faceplate) when spinning up the work for the first time.

If you need to machine close to a clamp, consider marking a safe limit circle on the faceplate and work with a marker pen to make it easier to see how close the cutting tool is to crash disaster.

The 65 mm cross-slide travel vs the 80 mm faceplate radius is a serious limitation that may require creative compound, toolpost and tool setups for larger parts.

Projects

Machined VESA mounting plate (left) and plate from Dell monitor stand it must match (right). The translucent washer shows the size of the original center hole.

My first faceplate project was boring out the center hole in a VESA mounting plate to adapt it to fit onto a surplus Dell 1708FP monitor stand. The part was centered using the tailstock dead center engaging with its original center hole. I clamped the part with studs and penny washers on the driving side of two opposite corners, with cap screws in the next slot round to trap the corners under the clamping washers, then withdrew the tailstock and dead center. After machining out the bore, I used the tip of the tool, rotating the chuck by hand, to scribe a circle for laying out the bolt holes. I finished off laying out and drilling the bolt and locating holes by hand at home, fitted it to the stand, and mounted the 2nd hand LG 24" widescreen monitor.

Current project: Thicknessing aluminum flat bar to make custom shims for the set of carbide insert tools, for the four way toolpost. The 8 mm shank tools need ~2.5 mm shim stacks, and the 6 mm shank tools need ~4.5 mm shim stacks. Ideally I'd machine single shims, but the only stock I've got handy cleans up to only 3.2mm, and some fine shimming may be needed to fine-tune the tool height.

After sorting out the clamps so they were no longer twisting the aluminum flat bar stock, and switching to the short 45° turning SCMT06204 insert tool in the four way toolpost, to improve rigidity and get a well controlled tip radius, the finish was much improved. I'm still having problems getting an even thickness and am getting approx. 0.05mm variation, I suspect due to the aluminium bar stock distorting due to internal stresses as its surface is cut away. ToDo: try supergluing the stock to the faceplate before clamping to further reduce chatter and stop the warping.

Thread Cutting

The objective is to cut a thread that complies with the ISO metric thread profile. Our lathe is not currently equipped to cut non-metric threads, (with the exception of BA which have pitches based on metric threads of that era).

Metric Thread Profile - from the geometry, H is ~86.6% of P

Metric thread data - See 'Preferred Sizes' at: https://en.wikipedia.org/wiki/ISO_metric_screw_thread

See "Mini Lathe User’s Guide" section Threading for general techniques *ONLY*, and above for change gears and threading dial setup.

External Threading

Initially turn work to required Major Diameter, set up change gears and threading tool, touch off on the work, zero the top and cross slide dials, and do a 'scratch' pass to check the pitch. Back off the tool, return the carriage, and re-engage the half nuts on a valid dial line clear of the end of the thread then immediately stop the lathe, and hand turn the chuck till the tool tip is (hopefully) over the scratch to check the thread pickup. If all is good, return the carriage again, restart the lathe and start cutting your thread.

Methods of doing so vary depending on the size of the thread and toughness of the metal, but straight-in plunge cutting is generally to be avoided as has the highest cutting forces, and does not reliably keep the carriage (and top-slide if set parallel to the work) loaded to avoid pitch errors due to backlash.

If leaving the half-nuts engaged and reversing the lathe to return to the start of the thread for the next pass, its absolutely essential to back the tool out of the thread for the return pass as it will not follow the path of the cutting pass due to backlash in the geartrain, leadscrew mounts and half-nuts.

Internal Threading

<nothing here yet>

Tooling and Tool Holders

Key dimensional data: The quick change holders accept up to 10 mm shank tools. The four way toolpost can clamp tools of up to 16 mm shank, but the slot base is only ~10.5 mm below the spindle center so cannot be used with >10 mm shank tooling unless it has a dropped tip. Large tooling with a centered tip is also problematic as you run out of height above the shank when trying to shim to match the spindle center height.

I'm currently working on getting the quick change toolpost and toolholders setup for easy use. The three toolholders came with cantilever height setting arms which historically haven't been installed as the supplied fixing screws were too short.

When fitting a toolholder, loosen off the dovetail clamp (socket headed screw on toolpost side opposite dovetail) till you can drop the toolholder onto it easily then gently wobble the toolholder with a finger on top of the height setting screw, as you tighten the dovetail clamp finger tight to ensure it seats at the preset height. Finally tighten firmly.

Unfortunately the OEM height setting screws foul the toolpost locking nut handle. Currently, if you need to swap toolposts you may have to first remove the quick-change holder from the post. There is enough nut handle swing to allow the quick change toolpost to be unclamped and rotated to fine set the tool angle without removing the toolholder. Unfortunately it seems the mating surfaces may be slightly out of square, as if you rotate the toolpost 90° or 180°, the nut swing may be insufficient to re-clamp it without removing the toolholder to do so. Adding a washer (M10?) under the locking nut helps if the handle ends up pointing in an undesirable direction. Can we make a taller nut of a similar pattern, to clear the height setting screws?

The quick change tool holders are significantly less rigid than the OEM four way toolpost. Therefore the four way toolpost should be used for the carbide insert tooling (set in silver case, see below). The four way toolpost requires shimming under the tool to set the tip height to the spindle center height - currently there's a fugly aluminum 'shim' stack that's fairly close for our HSS tools. Can we machine some single piece aluminum blocks to exact height to shim the set of insert tools?

HSS Tools

Our HSS tools are made from 8 mm square bar stock, hand-ground to tip profile in-house. I've installed our usual HSS LH turning and parting off tools in two of the quick change holders and set the heights correctly. There are a couple of other HSS tools or tool blanks knocking about. Taking heavy cuts turning steel (even with good cutting oil) blunts HSS tools fairly quickly, which are time-consuming to re-sharpen nicely without a dedicated tool & cutter grinder with appropriate jigs. Its worth noting that the usual 'speeds & feeds' tables are commonly based on surface speeds expected to give a half hour (active cutting) tool life before resharpening.

I touched up the LH turning tool by lapping on wet & dry (silicon carbide) paper on glass (Aka: 'Scary Sharp') working upwards through the grits 200, 400, 600 and finally 1000, initially 'bluing' the surfaces to be lapped with a marker pen to see which areas needed taking down more. The end of the tool was significantly uneven so I touched that up freehand on the bench grinder to flatten it when it became apparent that 200 grit lapping wasn't cutting where it needed to. There was an existing microbevel on the leading side, which I kept. Finally I 'dubbed' the leading corner vertical edge on the 1000 grit to give it a very slight radius. A test cut on brass gave a very nice finish when turning.

Tungsten Carbide Insert Tools

Decoding ISO insert tooling part numbers: https://www.cutwel.co.uk/blog/learn-the-turning-tool-iso-code-system

Our set of Tungsten carbide insert lathe tools
Tools, left to right, (+ last across top):
PartNo Description Insert Shank Shank H/mm Tip H/mm
SSKCR0610H06 75° through boring SCMT06204 Long 6 6.4
SWUCR0610H05 93° boring, deep facing WCMT050308 Long 6 6.35
SSSCR0610H06 45° boring, deep facing, internal chamfering SCMT06204 Long 6 6.4
SWGCR0810E05 90° RH turning, facing? WCMT050308 Short 8 8.7
SSSCR0610H06 45° turning, chamfering SCMT06204 Short 8 8.4
SSBCR0610E06 75° RH turning, chamfering SCMT06204 Short 8 8.4
LW0810R-04 60° external threading JCL15-120 Short 8 8.1
QA0812R-03 grooving, parting off CK3 Short 8 ~9.8
LN0813R-04 60° internal threading JCL15-120 Long 7.95 8.1 ?
More Tools, (loose in tin):
PartNo Description Insert Shank Shank H/mm Tip H/mm
QA0812R-03 grooving, parting off CK3 Short 8 ~9.8
Glanse SIR0012K11 60° internal threading bar 11IRA60 Long 12 dia ?

Chatter can rapidly kill carbide tooling by chipping the cutting edge. To improve rigidity and reduce the risk of chatter, the cross-slide and compound gib screws need to be well adjusted so there is minimal play in the slides, the four way toolpost kept over the cross-slide, and the work kept close to the chuck (or otherwise supported by tailstock or steady rest) to avoid excessive deflection.

Further investigation of the tool height situation is not encouraging - the so-called 'set' in question does not have a consistent tip height (see above table)! The insert seats *should* be machined allowing for the insert thickness to bring all the cutting edges to the same height with respect to the shank underside. However if you place them tip to tip on a table its easy to see there is considerable height variation, so they will need to be individually shimmed (or at best, one machined shim will only be right for two or three tools).

Inserts

I need to inventory and assess the existing inserts under magnification. Some are obviously badly chipped and thus either unusable or at least require rotation to expose a fresh cutting edge. We urgently need JCL15-120 and WCMT050308 inserts, and should get spares of the others.

Inserts used in set:

JCQ3 Insert

N.B. I cant find a UK supplier for CK3. RDG Tools seem to no longer have stock and have taken down their CK3 page. Some sources suggest RCJCQ3-0 or JCQ3 may fit but those are also difficult to find.

Inserts used in other tools:

  • 1x CK3 (as above) also missing from spare parting off tool
  • 1x 11IRA60 in Glanse threading bar + 1x spare

Cutting fluids

Why bother?

Simply watch this video and consider what's actually happening to that thin ribbon of metal being removed. Most of the lathe's motor power is being turned into heat by internal friction in the chip being removed in the zone around the cutting edge, and surface friction at, and immediately behind the cutting edge, near-instantly heating the chip by up to several hundred degrees. Reducing the surface friction using a suitable cutting oil reduces the strain on the machine as a whole, and reduces workpiece and tool heating (and thus expansion) with consequent improvements in maximum usable feed and depth of cut, and/or surface finish and accuracy. It also drastically increases the life of the cutting edge.

Practicalities

We don't have a coolant system for the lathe and *really* don't want the maintenance hassles of using soluble cutting oil/coolant as if used infrequently its a PITA to keep recirculated high water content cutting fluids from going rancid and stinky, and they can also rust the ways, so even a total loss gravity feed system is problematic. Therefore if dry machining doesn't give a good enough finish, we tend to use oil applied topically, by hand to the work.

  • Hard brass is typically free-turning without oil, however some light oil can improve surface finish, but with the disadvantage that it will increase loose chip buildup on the tool as hard brass typically forms short spalls or splinters rather than curly chips.
  • Many Aluminium alloys tend to be gummy, and Paraffin or other mineral spirits mixed with a little oil can help prevent the aluminum welding to the tool edge. WD40 will do at a pinch, but its messy to apply from a spray can.
  • Steel really needs *GOOD* cutting oil. We supposedly have some, but its certainly worth trying lard oil - the traditional choice for steel. If there are any objections to lard oil, although apparently butter Ghee can be used in place of lard (and is inoffensive to certain religious groups and most vegetarians) , we should bite the bullet and get some commercial dark high Sulphur cutting oil, but beware, many such oils use an additive package that includes lard oil.

I've sorted out an oil pot lid with a 1/2" brass collar soldered in to give a nice smooth sided hole, for ease of use and to minimize the risk of spills when using a brush to apply cutting oils, and got some dirt-cheap brushes. It fits Shippam's paste (and similar own-brand spread) jars and I've found several jars and ordinary lids to seal them for storage. Unfortunately it isn't the easiest to get this type of jars' lids back on square so they seal properly, and if you over-tighten them and there's a temperature change, they can be a total <expletive> to reopen. N.B. For the smaller brushes, the glue holding the bristles in is attacked by paraffin. To prevent loss of bristles, crimp the aluminum ferrule of each new brush of this type before use.

I've also got some paraffin wax (in the form of tealights), which it would be worth trying applied under power to brass and possibly Aluminium stock before each cutting pass, as it will make less mess than oil. Its unfortunately likely to be significantly less effective than a liquid as it wont flow unless the work or tool tip is heating up. ToDo: get a larger chunk/bar of wax, to avoid the need to hold it so close to the spinning chuck!

Cleaning and Maintenance

After use, brush all swarf off the toolholder, compound and cross slide etc. ways and leradscrew. Ian B has blocked off the opening at the headstock end of the rear splashguard (to try to keep swarf out of the motor), so one must sweep the chips towards the open tailstock end and catch them in a dustpan or similar. Preferably, also clean out the chip tray under the lathe.

Before engaging the half-nuts for power feed/threading, check the leadscrew is clean!

Caution: the traverse gears behind the carriage handwheel are in an open-backed housing and tend to become packed with swarf! Clean out as much as you can with a toothbrush ...

N.B. Lack of lubrication and/or swarf or dirt buildup can be disastrous:

  • If using the change gears/power feed, lack of lubrication of the B-C stub shaft center pin or either leadscrew end bearing can result in seizure and immediate destruction of one or more gears in the gear train or worse.
  • Small pieces of swarf can get between the saddle and ways, or into the slides degrading accuracy, possibly permanently if hard swarf scores them, or jamming them. The carriage handwheel gears behind the apron are notorious for accumulating swarf, and swarf buildup on the leadscrew can prevent the half-nuts engaging properly, resulting in scrapped work, and possibly stripped half-nuts.
  • Metal swarf can get into the motor (though Ian B has modified the rear chip catcher to reduce the risk) or into the electrical box via the leadscrew, and short-circuit stuff. At best it will blow the fuse and need a strip-down to clean it out, at worst it may require a replacement speed controller (currently £92) and/or motor (currently £105) and possibly other electrical parts.
  • Grit from grinding, sanding etc. forms a grinding paste with the way oil, and will rapidly wear out the ways, saddle and slides. Keep grit off at all costs e.g. by covering the ways and slides during grinding/sanding operations, and if there's any chance grit has gotten where it shouldn't, clean and re-lubricate *BEFORE* moving the carriage or slides, then move the carriage and slides, wipe down where they were with a clean paper towel and check there's no remaining traces of dirt other than clean way oil on the paper towel. If it doesn't come clean when you re-lubricate and move it again, a full strip down may be required to solvent clean and relubricate the precision sliding surfaces.

Lubrication

See section: "Lubrication" in LittleMachineShop.com "Mini Lathe User’s Guide" (below). As we usually only open two nights a week, in the table on page 16, Daily lubrication becomes Weekly and Weekly becomes Monthly.

Issues and Annoyances

As of November 2022

  • The leadscrew shaft is rubbing on the insulating separator inside the control box. Unfortunately the corner of the relay on the Filter Control Board (#160) doesn't allow enough clearance. Although the friction isn't much of a problem at high reduction ratios, e.g. 16:1 power feed, it increases the stress on the change gear train, and may be problematic when threading at feeds above 1:1. Possibly pack out the control box mountings by a couple of mm.
  • The high-low drive gear selector behind the headstock is incorrectly labeled and differs from the manual: low gear (which we normally use) is with the lever towards the tailstock. I suspect that the gears in the headstock were refitted the wrong way round when it was upgraded to metal gears.
  • The Carriage lock (vertical handscrew near the tailstock edge of the saddle, between the ways) sticks up enough that it fouls the top slide if the compound is aligned with the lathe axis (or indeed at any significant angle with respect to the cross slide) It has to be removed to get an axially aligned tool anywhere near the center axis, e.g. for a facing operation, just when you *don't* want an unlocked carriage. Its possible to demount it and temporarily replace it with a socket headed screw and an Allen key, but it really needs either an alternative locking system, or a fold-down handle. Currently, the handscrew has been replaced with a M5 bolt, to permit access when the top slide is over it. You'll need an 8mm spanner or nut-driver
  • The tailstock locking lever is loose and can be pulled out on its axis. It works OK when fully pushed home but needs investigating. I tightened the grub screw as the lever was coming off its shaft, but the whole shaft pushes/pulls in and out. It works OK fully pushed in, but it seems something that is meant to retain it has failed inside the tailstock base.
  • Change gear alignment is poor. I've currently got a gapped washer (to clear the key) packing out the A shaft so the gears line up, but this reduces the key's engagement so is problematic due to the high loading if the gears are set up for coarser threads. Also I need to turn down some penny washers to slightly less than the root diameter of the metal 20T pinions, as gear retaining washers. The gear retaining washers for A gear and B-C stub shaft are now done, turned down to slightly under 16 mm dia. Spares in the change gear tin. ToDo: The D (leadscrew) washer requires a larger center hole, so make two more with that hole.
  • The saddle gibs (actually the sheer plates) appear to be too loose, to the point that engaging a slightly stiff threading dial can cause it to self-feed, an obvious crash hazard if working near the chuck or a step in the work. I took the apron off for access (and to clean the carriage handwheel gears), and found the front sheer plate screws were completely loose. I've snugged them up some and set the opposing grub screws and got a lot of the slop out. The rear ones still need to be done.
  • The cross-slide screw has excessive backlash (nearly three turns), possibly due to end float, which increases the risk of loosing track of the cut depth during threading operations. If you end up off by a turn too far in, a crash is the most likely outcome.  Mostly Fixed 11/10/2022, see below.

    Possible backlash fix: https://youtu.be/Wu_tI29JL2Y?t=163 TLDR: measure flange on cross-slide screw and depth of recess in cross-slide bracket (behind dial) and machine a shim washer to take up nearly all the difference. Brass tinned with Pb-free solder to form a white metal bearing surface should work at least as well as the bronze used in the video.

    So it turns out that the reason the cross-slide had nearly 3mm of backlash was loose cross-slide screw nut mountings. It has two socket headed cap screws pulling up, one either end, easily accessible from the top of the cross-slide, which control the tilt of the nut to take up backlash in the nut, and an opposing grub screw pressing down on the center of the nut to make it longitudinally rigid.

    I gambled the cap screws weren't too far out and snugged up the grub screw, and that immediately took out over 95% of the backlash which is now down to 10 divisions or so, or 0.25mm. Shimming the cross-slide screw collar should take out some of what's left and careful adjustment of the nut tilt should get that down to under 0.1mm.
  • The chuck guard cant close with the faceplate on the spindle.  Resolved: The guard is now fitted with wing nuts so it can be removed allowing the the interlock switch to close when using the faceplate. It *MUST* be refitted if a chuck is fitted. The chuck guard is primarily there to make it very difficult to start the lathe without removing the chuck key and to reduce the area of large diameter spinning surface exposed. It may slow down the projectile if a chuck sheds a jaw but is unlikely to stop it. Also it serves to contain coolant spray spun off the chuck. As we don't use flood coolant this isn't an issue for us. As setting up for faceplate work doesn't use a chuck key, and the most hazardous zone is the face of the faceplate, with its spinning projecting clamps, with full access required for machining operations, which a guard would not cover, the consensus is that removing the guard is an acceptable risk.
  • The three jaw chuck and the faceplate aren't seating properly on the spindle nose. Its too tight on the register diameter of the lip. This results in grossly excessive runout, and also makes this chuck and the faceplate a PITA to fit or remove. Cleaning the spindle nose, and faceplate and chuck register recesses does not help. Currently fitting either to run reasonably true requires working round tightening the nuts on the studs gradually while tapping the chuck or faceplate home to the spindle nose seating surface with a rubber mallet paying particular attention to evening out the hairline gap between them as you do so. Removal is more rubber mallet work after backing off the nuts to the ends of the studs (to catch the chuck/faceplate when it comes loose), on the back of the faceplate, or for the chuck, on the back of the fully closed jaws via a thick aluminum bar through the center of the spindle as a drift (use the bar with somewhat mushroomed ends).

    Hammering on the chuck/faceplate like this is obviously bad for the spindle bearings, but they weren't that great to start with. A spindle bearing upgrade, probably to tapered roller bearings is becoming increasingly desirable.

    I have a proposal to resolve the chuck/faceplate seating issue (Telegram message to Ian B):

    On further thinking about the miss-fitting three jaw chuck, neither the four jaw chuck nor the faceplate require that precise alignment, as one always adjusts the work held by/on them to run true, so a tiny increase in their runout when mounted will be insignificant.

    As a replacement spindle is only £52 but a replacement 4" three jaw chuck is £120, the lowest risk cure for our excessively tight fitting chuck would be to turn down the register (outer) diameter of the lip (inner ring) of the spindle nose till the three jaw chuck just fits cleanly.

    As there's very little to be taken off, setting up a Dremel in a 3D printed adapter for toolpost grinding is probably the best approach.

    Ian B concurred:

    I'm in full agreement with your suggestion, to grind the lip of the spindle.

    Changing chucks should be easily done and having to whack the three jaw chuck to remove it can't be good for a lightweight lathe like ours.

    And you're saying the grinding bit of a Dremel will be adequate for the spindle? Perfect.

    TLDR: We are working on it!

Manuals, Books and other resources

Manuals

The RML CJ18A Mini-Lathe Induction Notes. Your mandatory Lathe Induction will cover most of this but its good to be able to refer back to it.

Official Amadeal CJ18A Manual, or paper copy kept on shelf above lathe.

The Conquest Super Lathe manual is considerably better than the Amadeal manual and is for a near-identical machine.

The Mini Lathe User’s Guide from LittleMachineShop.com is even more comprehensive, going into its usage in some detail, with a proper TOC, and covers both US and Metric versions of Realbull Mini-lathes. The only fly in the ointment is the threading section assumes a US lead screw so change gear selections and threading dial divisions will not be correct for our lathe.

Sieg C3 Mini-lathe Dismantling and Reassembly Guide "A picture story book to help you dismantle and reassemble your Sieg C3 Mini-Lathe" Is this near enough to ours to serve as a maintenance guide?

The motor controller is a clone of a KBIC® SCR DC Motor Speed Control

Books

Metal Turning on the Lathe, by David A Clark, Crowood Metalworking Guides, ISBN-13:‎ 978-1847975232 Kindle Edition (£8.99). A 'free' epub can be googled for, *NOT* linked here due to dubious legality.

Screwcutting In The Lathe, by Martin Cleeve (a pen-name of Kenneth C Hart), Workshop Practice series #3, ISBN-13: 9780852428382

Workholding in the Lathe, by 'Tubal Cain' (a pen-name of Tom Walsh), Workshop Practice series #15, Argus Books, ISBN-10: 0852429088

Metalwork and Machining Hints and Tips, by Ian Bradley, Workshop Practice series #20, ISBN-13: 9780852429471

Tool and Cutter Sharpening, by Harold Hall, Workshop Practice series #38, ISBN-13: 9781854862419

Cutting Fluids, by EC Bingham, NIST Tech. Paper No. 204, 1921

WWW resources

There's a *LOT* of mini-lathe info online. Notable sites include:

Youtube Playlists & Videos

  • Blondihacks: Lathe Skills (playlist) - "This is an educational series to help you learn to use your metal lathe. Watch them in order for best results! Satisfaction not guaranteed, especially if you're a cranky sort of person."
  • Frank Hoose (mini-lathe.com): Mini Lathe Overview (playlist)

Forums

with publicly accessible archives